#! /usr/bin/env python ###################################################################### # Written by Kevin L. Sitze around 2008-05-03 # This code may be used pursuant to the MIT License. ###################################################################### """Generate classes with named data attributes that can be sequenced. Useful for POD classes for which many instances will exist. Compare this feature set to NamedTuples by Raymond Hettinger: http://code.activestate.com/recipes/500261-named-tuples/ >>> Point = NamedSequences('Point', 'x', 'y') >>> Point # module.class >>> Point.__doc__ # documentation 'Point(x, y) => instance' >>> Point() # default fields are undefined Point(x = None, y = None) >>> Point = NamedSequences('Point', 'x', y=0) # specify new defaults >>> Point() # default fields take our values Point(x = None, y = 0) >>> Point(1, 2) # positional parameters Point(x = 1, y = 2) >>> p = Point(y=3, x=4) # keyword parameters >>> p Point(x = 4, y = 3) >>> p.x # member access and... 4 >>> p[0] # ...indexing and... 4 >>> p[1] 3 >>> p[2] # ...bounds checking Traceback (most recent call last): [snip] IndexError: tuple index out of range >>> x, y = p # unpack on assignment >>> x, y (4, 3) >>> d = p._asdict() # as dictionary >>> d {'y': 3, 'x': 4} >>> Point(**d) # from dictionary Point(x = 4, y = 3) >>> p._replace(x=10) # replace fields by name Point(x = 10, y = 3) """ import keyword import copy import sys __all__ = ( 'NamedSequences', 'named_sequences' ) def unique( it ): """unique( it ) => iterator Generate each value from the input iterator "it" exactly once ordered according to the first occurance of the value. """ seen = set() for v in it: if v in seen: continue seen.add( v ) yield v def NamedSequences( className, *_names, **_kwds ): """NamedSequences( className[, 'name_1'[,...[, name_N = defaultValue_1[, ... ]]]] ) Construct a new class that contains only the named elements. This is useful in cases where you know you're going to have a ton of instances for a class and wish to conserve memory by avoiding the overhead of a per instance dictionary. Instances of the returned class are Python sequences. NamedSequences( __name__, 'MyClass', 'fieldName1', ..., # argument field names fieldNameN = defaultValue1, ...) Keyword arguments are unordered dict's so if you wish to control field ordering you MUST specify your field names twice, once in the positional argument list area (to define the ordering), and the second time in the keyword area to specify that field's default value. Field names defined only as keyword arguments are placed in ascending order after all field names specified as positional arguments. Duplicate field names are dropped with priority given to the first appearance of the name. Keyword arguments beginning and ending with a double underscore are Python reserved words. These will be inserted directly into the class __dict__ rather than added as regular field names. For example you can redefine the module that the class belongs to using the following pattern: Point = NamedSequences('Point', 'x', 'y', __module__ = __name__ ) though this is actually redundant as the default is the module from which this function was called. You can even specify your own documentation for the class using "__doc__ = ''". """ # versatile arguments: (klass, 'x y'), (klass, 'x', 'y') or (klass, 'x,y') if len( _names ) == 1 and isinstance( _names[0], basestring ): _names = _names[0].replace( ',', ' ' ).split() _names = tuple( map( str, _names ) ) def is_identifier( s ): try: class Tmp( object ): __slots__ = (s,) except TypeError: return False else: return not keyword.iskeyword( s ) if not is_identifier( className ): raise ValueError( 'class name "%s" is not a valid identifier' % className ) for name in _names + tuple( _kwds.keys() ): if not is_identifier( name ): raise ValueError( 'field name "%s" is not a valid identifier' % className ) # Extract Python reserved words extras = dict( ( k, v ) for k, v in _kwds.iteritems() if k.startswith( '__' ) and k.endswith( '__' ) ) _kwds = copy.deepcopy( _kwds ) # no messing with defaults for k, v in extras.iteritems(): _kwds.pop( k ) # remove reserved words try: extras.setdefault( '__module__', sys._getframe( 1 ).f_globals.get( '__name__', '__main__' ) ) except ( AttributeError, ValueError ): pass # no getting at the module in this env... _slots = tuple( unique( _names + tuple( sorted( _kwds.keys() ) ) ) ) # there can be only one... class SequenceClass( object ): """This class is the superclass of the class generated by "NamedSequences". Each call to "NamedSequences" creates a new "SequenceClass" superclass. """ __slots__ = () def __init__( self, *argv, **kwds ): for n, v in zip( _slots, argv ): setattr( self, n, v ) # apply positional args 1st for n, v in kwds.iteritems(): setattr( self, n, v ) # apply keyword args 2nd def __cmp__( self, other ): if self.__class__ is other.__class__: return cmp( tuple( self ), tuple( other ) ) else: raise TypeError, "requires a '%s' object but received a '%s'" % ( self.__class__.__name__, other.__class__.__name__ ) def __getattr__( self, n ): """Defer applying class defaults until they are actually needed""" try: result = _kwds[n] except KeyError: if n in _slots: result = None else: raise object.__setattr__( self, n, result ) return result def __getitem__( self, i ): return getattr( self, _slots[i] ) def __getnewargs__( self ): return tuple( self ) def __setitem__( self, i, v ): setattr( self, _slots[i], v ) def __iter__( self ): return iter( getattr( self, n ) for n in _slots ) def __len__( self ): return len( _slots ) def __repr__( self ): return self.__class__.__name__ + '(' + ', '.join( n + ' = ' + repr( getattr( self, n ) ) for n in _slots ) + ')' def __str__( self ): return self.__class__.__name__ + '(' + ', '.join( repr( getattr( self, n ) ) for n in _slots ) + ')' def _asdict( self ): return dict( ( n, getattr( self, n ) ) for n in _slots ) def _replace( self, **kwds ): return type( self )( *self, **kwds ) klass = SequenceClass extras.setdefault( '__doc__', '%s%s => instance' % ( className, repr( _slots ).replace( "'", "" ) ) ) extras.update( { '__name__': className, '__slots__': _slots } ) return type( klass )( className, ( klass, ), extras ) def named_sequences(func): """Decorate a function definition to create the tuple. @named_sequences def Point(x, y): pass """ return NamedSequences( func.__name__, *func.__code__.co_varnames ) if __name__ == '__main__': import traceback def assertEquals( exp, got ): """assertEquals(exp, got) Two objects test as "equal" if: * they are the same object as tested by the 'is' operator. * either object is a float or complex number and the absolute value of the difference between the two is less than 1e-8. * applying the equals operator ('==') returns True. """ from types import FloatType, ComplexType if exp is got: r = True elif ( type( exp ) in ( FloatType, ComplexType ) or type( got ) in ( FloatType, ComplexType ) ): r = abs( exp - got ) < 1e-8 else: r = ( exp == got ) if not r: print >>sys.stderr, "Error: expected <%s> but got <%s>" % ( repr( exp ), repr( got ) ) traceback.print_stack() def assertException( exceptionType, f ): """Assert that an exception of type \var{exceptionType} is thrown when the function \var{f} is evaluated. """ try: f() except exceptionType: assert True else: print >>sys.stderr, "Error: expected <%s> to be thrown by function" % exceptionType.__name__ traceback.print_stack() def assertFalse( b ): """assertFalse(b) """ if b: print >>sys.stderr, "Error: expected value to be False" traceback.print_stack() def assertTrue( b ): if not b: print >>sys.stderr, "Error: expected value to be True" traceback.print_stack() #### # Test NamedSequences #### Point = NamedSequences( 'Point', 'x', 'y' ) assertEquals( "", repr( Point ) ) assertEquals( 'Point(x, y) => instance', Point.__doc__ ) p = Point( 0, 1 ) q = Point( y = 0, x = 1 ) assertEquals( 0, p[0] ) assertEquals( 0, p.x ) assertEquals( 1, p[1] ) assertEquals( 1, p.y ) assertEquals( 1, q[0] ) assertEquals( 1, q.x ) assertEquals( 0, q[1] ) assertEquals( 0, q.y ) assertException( IndexError, lambda: p[2] ) x, y = p assertEquals( p[0], x ) assertEquals( p[1], y ) x, y = q assertEquals( q[0], x ) assertEquals( q[1], y ) d = p._asdict() r = Point( **d ) assertEquals( p, r ) s = r._replace( x = 5 ) assertEquals( 5, s.x ) assertEquals( r.y, s.y ) s = s._replace( y = 6 ) assertEquals( 5, s.x ) assertEquals( 6, s.y ) assertEquals( 'Point', Point.__name__ ) assertEquals( 'Point', p.__class__.__name__ ) p = Point() q = Point() assertEquals( q, p ) assertEquals( 0, cmp( p, q ) ) p.x = 1 q.x = 2 assertTrue( p < q ) assertTrue( q > p ) assertTrue( cmp( p, q ) < 0 ) assertTrue( cmp( q, p ) > 0 ) p.x = 1 q.x = 1 assertEquals( 0, cmp( p, q ) ) assertEquals( 0, cmp( q, p ) ) p.y = 1 q.y = 2 assertTrue( cmp( p, q ) < 0 ) assertTrue( cmp( q, p ) > 0 ) assertEquals( 'Point(1, 1)', str( p ) ) assertEquals( 'Point(x = 1, y = 1)', repr( p ) ) assertEquals( p, Point( x = 1, y = 1 ) ) p.x = '1' assertEquals( "Point('1', 1)", str( p ) ) assertEquals( "Point(x = '1', y = 1)", repr( p ) ) Point = NamedSequences( 'Point', x = 1, y = 2 ) p = Point() assertEquals( 1, p.x ) assertEquals( 2, p.y ) Point = NamedSequences( 'Point', 'x y' ) p = Point() p.x = 0 p.y = 1 Point = NamedSequences( 'Point', 'x,y' ) p = Point() p.x = 0 p.y = 1 assertException( KeyError, lambda: p.z ) assertException( AttributeError, lambda: setattr( p, 'z', 1 ) ) Point = NamedSequences( 'Point', x = 0, y = 0, __module__ = '__name__' ) assertEquals( "", repr( Point ) ) assertException( ValueError, lambda: NamedSequences( 'for' ) ) assertException( ValueError, lambda: NamedSequences( 'in' ) ) assertException( ValueError, lambda: NamedSequences( '123' ) ) assertException( ValueError, lambda: NamedSequences( 'test', 'for' ) ) assertException( ValueError, lambda: NamedSequences( 'test', 'in' ) ) assertException( ValueError, lambda: NamedSequences( 'test', '123' ) ) @named_sequences def Point(x, y, z): pass p = Point() p.x = 0 p.y = 1 p.z = 2